Since Shiga Prefecture lies between areas that meet and do not meet the environmental quality standards for the substance PM_2.5 , it is important to determine its characteristics there. Unfortunately, insufficient data on PM_2.5 has been collected for Shiga Prefecture. In this study,PM_2.5 and PM_C (coarse particulate matter) were collected in filters at Seta Hill in Shiga Prefecture from January 2013 to December 2014 and their inorganic components were analyzed. The main components of PM_2.5 were SO₄^2- and NH₄^＋, whereas PM_C mainly consisted of cations such as Na⁺ and Ca²⁺. There was a strong positive correlation between SO₄^2- and NH₄⁺. Although the variation of NH₄^＋was usually connected to that of nss-SO₄^2- (non-sea salt sulfate), the concentration of nss-SO₄^2- in Summer of 2013 was higher than usual due to the eruption of Mt. Sakurajima and weather conditions such as high temperature and low wind. The average equivalent ratio of NH₄^＋/SO₄^2- during the observation period was 0.79. This value was higher than that at Cape Hedo, Okinawa Prefecture (0.56) and lower than that in the urban area of Otsu City, Shiga Prefecture (1.32). It is surmised that the differences are due to the influences of domestic urban sources of NH₄⁺and local sources of NH₄⁺, such as automobile exhaust gases.

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